14 THOMAS SAY FOUNDATION 
soon learns to pick out the nymphs which are approaching emer- 
gence. At the time of transformation the nymph crawls up on 
the screen out of the water and after the adult has emerged 
the nymphal skin remains attached to the screen. The adult and 
nymphal skins may then be placed together in a vial of alcohol 
and preserved for study. Where an outdoor natural stream is not 
available for rearing purposes, the nymphs, if quite mature, can 
sometimes be reared by keeping them in moist sphagnum. Frison 
(6) reared a number of nymphs in small tins containing moist 
leaves. Aquaria, in which the water does not get too warm, and 
through which a constant stream of air is kept flowing, may also 
be utilized for rearing. Tap water is, in most eases, toxic to the 
nymphs, and therefore cannot be used. 
PRESERVATION FOR STUDY 
The most satisfactory manner of preserving nymphs for study 
is to place them in 80 to 85% alcohol. Pinning or preserving the 
nymphs or nymphal skins dry is not satisfactory since the gills 
and the other delicate structures shrivel up so badly that identifi- 
cation becomes difficult or impossible. Alcohol tends to fade out 
the colors to some extent but usually not sufficiently to make 
determination impossible. Nymphs which are to be examined for 
food contents should be placed in alcohol or in a 4% formalin 
solution immediately after being taken from the water. Identifica- 
tion of the intestinal contents will be easier if examination is 
made as soon as possible after the specimens have been brought 
to the laboratory. If this is not feasible, the nymphs should be 
slit before they are placed in the preservative to insure ee 
preservation of the food contents of the intestine. 
TECHNIQUE 
The technique involved in the study of stonefly nymphs is 
quite simple. In most instances it is possible to recognize the 
genera, aS well as many of the species, by examining the entire 
specimen under the binocular microscope, while the larger species 
ean often be identified with a simple lens, or even with the un- 
aided eye. In some specimens, identification to genus can readily 
be made by a study of the details of tracheation or of venation. 
In such eases it is usually better to cut off the wing pads and 
mount them on slides. The wing pads may be readily snipped 
off with a sharp scalpel, a razor blade, or with a pair of fine- 
